b 1.Field of the Invention
This application is directed to a UV-base ceramic paint composition and a method of forming a glass sheet with a UV-base ceramic paint thereon. The UV-base ceramic paint composition is one which does not stick to fiberglass materials at elevated temperatures when the fiberglass is brought into contact therewith. The method of forming the glass sheet is one which allows a UV-base ceramic painted glass sheet to be contacted by a fiberglass covered forming die which forms the glass in a heated condition into a desired shape. The forming operation may be carried out without any sticking of the UV-base ceramic paint to the fiberglass forming die.
2. Description of Related Art
Ceramic paint compositions are generally well known to the skilled artisan. These ceramic paint compositions can be used, for example, to form borders around the edges of glass sheets which are used as windshields, side lites and back lites in motor vehicles.
Such ceramic paints usually include a mixture of metal oxides, which together act as a coloring agent for the ceramic paint. The metal oxides are nonreactive with one another and nonreactive with any elements or compounds they normally come in contact with while being heated to temperatures up to about 1300.degree. F. The mixture of metal oxides can be controlled so as to get a selected color from the ceramic paint composition. Normally, in automotive applications, the selected color is black, although shades of gray are now becoming popular.
Such ceramic paint compositions also include a low melting point glass frit which generally melts at a temperature below 1300.degree. F. The low melting point glass frit is the material which bonds the mixture of metal oxides to the glass sheet and ensures that it remains after the glass sheet has been cooled back to room temperature. A vehicle is normally mixed with the metal oxides and low melting point glass to allow the ceramic paint composition to be applied in a paint application process. For example, if the paint application process is a silk screen printing operation, the vehicle can be a UV-base organic medium for carrying the other materials during the silk screen printing operation.
Many different types of ceramic paint compositions of the above general type are well known to skilled artisans. The exact metal oxides, low melting point glass frit, and UV-base vehicle selected for such Paint are well within the skill of artisans in this area. The manner in which the different materials may be varied in order to achieve the results desired in a particular application is also well within the skill of an artisan.
As was discussed in my recently issued patent, U.S. Pat. No. 4,596,590, I found, in the situation where a sheet having a ceramic paint thereon was contacted by a fiberglass forming die, that paints of the above-described general composition had a great tendency to stick on the fiberglass covered die. The sheet of glass, of course, was being heated to an elevated temperature, generally less than 1300.degree. F., so that it may be engaged by a forming die and formed into a configuration other than flat.
As further discussed in my patent '590, the difficulty arose that the ceramic paint compositions generally known to skilled artisans would not operate in a glass forming process in which a heated glass sheet containing the ceramic paint composition was engaged by a fiberglass covered forming die. As I disclosed in my patent, no other materials are known for covering the forming die because the fiberglass is the only material which will withstand the heat and rigorous requirements of the environment to which it is subjected. Other materials that have been used to cover forming dies quickly break down and wear out when repeatedly brought into engagement with the surface of a heated glass sheet. Thus, fiberglass is the material which is used to cover forming dies and this material, unfortunately, sticks to ceramic paint compositions then known to skilled artisans when those compositions are heated to an elevated temperature which is necessary to form glass by a forming die.
In my patent '590, I disclosed a method of forming glass sheets with a ceramic paint thereon which could withstand the high temperatures and repeated engagements of painted glass sheets by the same forming die without paint sticking to the forming die. I solved the problem by adding to the ceramic paint, as a new component thereof, a metal oxide having a low valence oxidation state and a high valence oxidation state. The metal oxide is in its low valence state when applied to the ceramic paint. My patent taught that I believed, when this metal oxide powder is subjected to a heating operation, that a portion of the powder on the upper surface of the ceramic paint composition readily oxidizes to form an excellent, fully oxidized metal oxide barrier across the top surface of the paint which insulates the low melting point glass frit and isolates the same from the fiberglass cloth. In particular, I taught that stannous oxide was an excellent metallic oxide powder to use.
In carrying on additional work in this area, particularly in working with UV-base ceramic paints, I found that the utilization of stannous oxide did have some drawbacks. In a UV-base system, when stannous oxide is present in the paint in an amount greater than 20% by weight or so, there is some tendency for the paint to stick on the fiberglass cloth when a large amount of pressure is applied to the painted glass sheet in a bending operation.
In a subsequently issued patent of mine, namely, U.S. Pat. No. 4,684,388, issued Aug. 4, 1987, I disclosed a method of forming a glass sheet with a UV-base ceramic paint thereon. In the method disclosed in my '388 patent, the following steps were carried out. A UV-base ceramic paint is applied to a glass sheet. The UV-base ceramic paint includes normal ceramic paint components along with, as a new component thereof, finely divided zinc metal powder and finely divided stannous oxide powder. The glass sheet is subjected to UV radiation and then heated to a temperature which softens the glass sheet sufficiently so that the glass sheet can be formed. The glass sheet and the ceramic paint thereon are engaged with a fiberglass covered forming die to form the heated glass sheet to a desired shape. The forming die is removed from engagement with the glass sheet. The finely divided zinc metal powder and finely divided stannous oxide powder addition to the ceramic paint is credited with being effective to prevent sticking of any ceramic paint to the forming die. The glass sheet is cooled to obtain a formed glass sheet with a ceramic paint thereon.
It is an object of this invention to provide a nonstick ceramic paint containing only one additive to achieve the nonstickability of that paint.
It is a feature of this invention to have a nonstick ceramic paint to which only a single material has been added to achieve the nonstickability thereof.
It is an advantage of this invention that only a single addition is made to a ceramic paint in order to achieve nonstick characteristics therefor.
It is an object of this invention to provide a method of forming a glass sheet having a UV-base ceramic Paint thereon in such a manner that the paint does not stick to a forming die.
It is a feature of this invention that a method is provided for forming a glass sheet having a UV-base ceramic paint thereon in such a manner that the paint does not stick to a forming die.
It is an advantage of this invention that a method is provided for forming a glass sheet having a UV-base ceramic paint thereon in such a manner that the paint does not stick to a forming die.